Intra-annual seasonal variability of surface zooplankton distribution patterns along a 110°E transect of the Southern Ocean in the austral summer of 2011/12Intra-annual seasonal variability of surface zooplankton distribution patterns along a 110°E transect of the Southern Ocean in the austral summer of 2011/12Intra-annual seasonal variability of surface zooplankton distribution patterns along a 110°E transect of the Southern Ocean in the austral summer of 2011/12

Seasonal cycles can provide insight into the interactions between zooplankton and the environment. However, few intra-annual seasonal studies have been undertaken in the Southern Ocean. We investigated the composition, distribution, and abundance of micro- and meso-zooplankton along the 110°E meridian with three transects in December 2011, January and March 2012 using a Continuous Plankton Recorder. High zooplankton abundance was recorded in the Polar Frontal Zone (PFZ) and the Antarctic Zone (AZ) in both day and night at all transects with 179.0–300.9 ind. m−3. The small copepods Oithona similis, Ctenocalanus citer, and copepodites indet (copepod indeterminable) were dominant in the PFZ and AZ communities. Total zooplankton abundance was comparatively consistent among transects. Nighttime abundance levels remained high in the AZ in March with high abundance of copepodites indet. This seasonal fluctuation appeared to be influenced by recruitment of new populations. Most core species/taxa, except for O. similis, C. citer, and foraminiferans in the AZ area in early January, exhibited a diel decrease in abundance. A multi-ship intra-annual seasonal survey will help detect their various regional and/or seasonal distribution patterns, and the impacts of environmental change on Southern Ocean pelagic ecosystems.日本南極地域観測隊がモニタリング観測を実施している南大洋東経110度において、連続プランクトン採集器（CPR）を用いた動物プランクトン群集組成、分布特性、現存量の季節変動調査を行った。試料は主要な海洋前線である亜南極前線（SAF）と南極前線（PF）を跨いだトランセクトにおいて、砕氷艦しらせで2011年12月と2012年3月、東京海洋大学練習船海鷹丸で2012年1月の計3回の曳航により得た。SAFとPFの間の南極前線域（PFZ）とPF以南の南極域（AZ）において動物プランクトンの高現存量を観測した。中でも小型カイアシ類のOithona similisとCtenocalanus citerが優占して出現した。3月のAZにおいてカイアシ類のコペポダイト幼生期の出現割合が高く、新規個体群の加入の影響と考えられた。本研究のような時系列データの取得は、動物プランクトンの多様な分布パターンを検出するとともに、彼らの環境変化への応答を探るうえで重要な情報集積となる。